Synthetic studies towards oxygenated and unsaturated furanocembranoid macrocycles. Precursors to plumarellide, rameswaralide and mandapamates

A new approach to the synthesis of oxygenated furanocembranoids, exemplified by danielid 3, is described. The approach features an intermolecular Knoevenagel-type condensation together with an intramolecular aldolisation to elaborate the furan and the lactone rings, respectively, in the initial target compound 14. Efforts to isomerise the C13–C14 double bond, or to introduce an alkene bond at C11–C12 in 14, leading to structures 3 and 8, respectively, are described.